Apparatus for making films



April 20, 1937. R. HERNDON APPARATUS FOR MAKING FILMS F'iied Feb. 5, 1935 INVENTOR Lee Roy Herndon ATTORNEY.

Patented Apr. 20, 1937 UNITED STATES PATENT QFFEQE APPARATUS FOR MAKING FILMS Lee Roy Hcrndon, Richmond, Va., assignor, by mesne assignments, to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application February 5, 1935, Serial No. 5,095

4 Claims.

5 ticularly, it relates to the continuous production of such films having a smooth, uniform surface substantially free from blemishes, and to apparatus for producing the same. The invention will be described in terms of cellulose regenerated 10 from viscose although it is to be understood that it is equally applicable to cellulose regenerated from other materials such as cuprammonium cellulose or to the production of cellulose esters and ethers by casting into a coagu- 15 lating bath. It is also applicable to the produc- 5 alkaline viscose, the "spent bath was discarded or bucked up by continuously adding concentrated new bath. This was rather unsatisfactory in that the film underwent a continuous change in quality coincident with changes in 30 strength of the coagulating acid. To overcome these difficulties, it was deemed desirable to use a continuously flowing coagulating and/or regenerating bath so that said bath would be at all times substantially uniform in composition. As

35 the demand for regenerated cellulose sheet materials increased, it became desirable to increase the speed of the machines which were used for the continuous production, including the various treating and drying steps, of these sheets. With 40 the introduction of these higher speeds, certain difficulties arose. For example, it became necessary to increase the speed of flow of the coagulating bath. With this increased flow, the coagulating bath became more and more agitated so 45 that the film of viscose as it emerged from the casting hopper often became distorted due to this agitation, with the result that the finished film showed fine striations, known as streaks.

An object of this invention is to produce non- 50 fibrous sheet materials having a smooth, uniform surface substantially free from streaks. Another object is an apparatus for producing the same. A still further object is to produce regenerated cellulose sheets or films having a smooth, uniform 55 surface substantially free from streaks and apparatus for producing the same. Other objects will appear hereinafter.

These objects are accomplished in general by extruding a coagulable liquid from a hopper through an elongated orifice into a coagulating bath, the coagulating bath immediately around the said orifice being protected from agitation by means of baffle plates, conveniently attached to the hopper.

The invention will be more clearly understood by reference to the following description taken in connection with the accompanying drawing, in which:

Fig. 1 shows a longitudinal cross section of a coagulating bath and a hopper embodying a pre ferred form of this invention;

Fig. 2 shows a detail of Fig. 1;

Fig. 3 shows a fragmentary side elevation of the hopper.

Referring to the drawing, a viscose solution 2 contained in a hopper 3 is extruded under pressure through the hopper lips l in the conventional manner. The'hopper lips d are immersed in the coagulating bath 5, so that the viscose is coagulated immediately upon issuing from the hopper lips 4. The coagulating bath is kept continuously flowing by means of inlet pipe 6 and exit pipe I, to which may be connected an overfiow pipe 8 as shown in order to keep the coagulating bath liquid level constant. In consequence of agitation of the coagulating bath resulting from this continuous flow, there are provided, according to this invention, two baffle plates 9 lying longitudinally of the hopper lips 4 and two baffle plates l lying transversely of the hopper lips 4. These baffle plates so enclose the hopper lips that coagulating bath can only reach and be abstracted from the vicinity of said lips through extended opening I! at the lower edges of the baflle plates 9 and IEI, thus preventing the disturbance of the freshly coagulated film by the coagulating bath until after it has been firmly set. The distance that the film will have to go' before being firmly set will depend upon several factors as hereinafter described. After being firmly set, the coagulated film l2 passes down over premier roll I3, up through the coagulating bath and over the carrier roll I l, after which it goes on to further treatments such as are well known in the art.

Referring now to Fig. 2, the baffle plates 9 are attached to the hopper lips 4 by means of the bolts l5. The essential or bottom edge l6 of the hopper lips 4 extends below the surface of the coagulating bath so that the essential edge l6 of the hopper lips 4 lies a short distance from the points I! of closest approach of the two baffle plates 9. This distance will be found to vary with the conditions, depending upon the rate of flow of the bath, the speed of casting, the ripeness of the viscose, the strength of the coagulating bath and other factors. In practice, a distance of 1" has been found convenient. It should not be so great that a large amount of coagulating bath is allowed to become stagnant in this area, nor so small that the film reaches the agitated area of the bath before becoming fully set. Likewise, the distance between points ll will vary with some or all of these factors. It should be great enough so that neither will the confined bath become too stagnant, nor the film be interfered with, and it should be small enough so that deleterious agitation of the confined bath will not take place.

The baflle plates have been shown of such a form that a greater quantity of coagulating bath is confined thereby than with vertical baflles,

' separated by the distance between points l1.

Useful effects may be obtained by means of this preferred form. It is to be understood that any other convenient form of bafile plates may be used.

In Fig. 2, it will be seen that there is an air space between the baffie plates 9 and the hopper lips 4. Holes I8 may be bored through the baffle plates 9 in order to ventilate the air space. The baflle plates may also be provided with hinges IQ of any desired nature so that the baffle plates can be swung back out of position when the machine is first started up and to allow easy access to the hopper lips for cleaning and other purposes. Springs 22 acting against the movable portions of baffle plates 9 force the plates inwardly against stops 23 to maintain the baffle plates in operative position.

Referring to Fig. 3, baffie plates ll! extend transversely of the ends of the hopper lips 4. It is ordinarily sufficient if these baffles be merely vertical plates, attached to the hopper by bolts 20 and in close juxtaposition to plates 9. If desired, plates It! may also be provided with holes 2| for the same purpose as holes l8. Baffle plates l may also be of any other convenient form, such as the form of plates 9.

In the practice of this invention the coagulating bath may be of any suitable composition and may accomplish both coagulation and regeneration of the viscose into cellulose, such as by means of a sulfuric acid-sodium sulfate bath or it may consist of a composition which will 00- agulate only, such as an ammonium sulfate bath, leaving the regeneration to a subsequent bath.

The bafile plates may consist of any desired material, such as aluminum or nickel, which will not be deleteriously affected by the coagulating bath.

By the practice of this invention, regenerated cellulose film, having a greatly improved smoothness, uniformity and freedom from streaks, can be produced efficiently without the use of expensive added equipment and without substantially changing the design of the film casting machines now in use. In addition, it has been found that the provision of a stagnant zone of coagulating liquid around the hopper lips makes it possible to run the casting machines for longer periods of time before it becomes necessary to clean and/or repair the hopper lips.

While I have described this invention with respect to the casting of cellulose films regenerated from viscose, it is obvious that it may be applied to any method of casting films which uses a set of hopper lips or their equivalent and casts directly into a continuously flowing coagulating bath. Such a method is applicable, for example, to the casting of lowly esterified and lowly etherified cellulose derivatives, particularly in those cases where it is desirable to obtain a final product which is free from streaks or other imperfections which might be produced from the coagulating bath. It is also applicable to the manufacture of continuous tubes or other forms of cellulose pellicles by an extrusion process, such as the manufacture of seamless sausage casings from viscose.

My invention is not limited to the specific procedure and apparatus described above, but is intended to include within its scope any modification or variation which conforms to the spirit of the invention.

I claim:

1. Apparatus adapted for the production of transparent pellicles suitable for use as wrapping tissue from cellulosic solutions and the like, comprising a coagulating bath, means associated therewith for maintaining a predetermined level of coagulating bath liquid, a hopper adapted to contain a cellulosic solution or the like and having an elongated extrusion orifice at its lower end, said orifice being so disposed with respect to the coagulating bath as to be submerged in the coagulating bath liquid during the filmforming operation, and baffle plates attached to said hopper and surrounding said orifice, two of said baffle plates being oppositely disposed and parallel to said orifice, whereby to eliminate the formation of streaks in said pellicles, said baffle plates having openings for ventilation of the space above said bath and surrounded by said baflle plates.

2. Apparatus adapted for the production of transparent pellicles suitable for use as wrapping tissue from cellulosic solutions and the like, comprising a coagulating bath, means associated therewith for maintaining a predetermined level of coagulating bath liquid, a hopper adapted to contain a cellulosic solution or the like and having an elongated extrusion orifice at its lower end, said orifice being so disposed with respect to the coagulating bath as to be submerged in the coagulating bath liquid during the film-forming operation, and bafile plates attached to said hopper and surrounding said orifice, two of said baffle plates being oppositely disposed and parallel to said orifice and converging downwardly towards each other under said hopper whereby to form a restricted passage in the coagulating bath beneath said orifice, whereby to eliminate the formation of streaks in said pellicles, said converging baffle plates being hinged to permit movement away from said orifice.

3. Apparatus adapted for the production of transparent pellicles suitable for use as wrapping tissue from cellulosic solutions and the like, comprising a. coagulating bath, means associated therewith for maintaining a predetermined level of coagulating bath liquid, a hopper adapted to contain a. cellulosic solution or the like and having an elongated extrusion orifice at its lower end, said orifice being so disposed with respect to the coagulating bath as to be submerged in the coagulating bath liquid during the filmforming operation, and bafile plates attached to said hopper and surrounding said orifice, two of said baflie plates being oppositely disposed and parallel to said orifice and converging downwardly towards each other under said hopper whereby to form a restricted passage in the coagulating bath beneath said orifice, whereby to eliminate the formation of streaks in said pellicles, said converging baflle plates being hinged to permit movement away from said orifice, and being provided with means for positively holding said baiile plates in operative position.

4. Apparatus adapted for the production of transparent pellicles suitable for use as wrapping tissue from cellulosic solutions and the like, comprising a coagulating bath, means associated therewith for maintaining a predetermined level of coagulating bath liquid, a hopper adapted to contain a cellulosic solution or the like and having an elongated extrusion orifice at its lower end, said orifice being so disposed with respect to the coagulating bath as to be submerged in the coagulating bath liquid during the film-forming operation, and baflle plates attached to said hopper and surrounding said orifice, two of said baffle plates being oppositely disposed and parallel to said orifice and converging downwardly towards each other under said hopper whereby to form a restricted passage in the coagulating bath beneath said orifice, whereby to eliminate the formation of streaks in said pellicles, said converging bafiie plates being hinged to permit movement away from said orifice and being provided with spring means for positively holding said baffle plates in operative position.

LEE ROY HERNDON. 

